The present invention relates to an optical system for an observing equipment such as a binocular or a terrestrial telescope that has an image-vibration compensation system.
Recently, binoculars provided with image-vibration compensation systems for preventing vibration of observed image due to a hand-held shake of a user have been developed. Japanese Laid Open Publication No. HEI 6-43365 discloses an image-vibration compensation system of a binocular that employs a variable angle prism for each of telescopic optical systems of the binocular. A variable angle prism is located between an objective lens and an erecting system. When the optical system vibrates due to a hand-held shake of a user, the vertex angle of the variable angle prism is controlled to stabilize the image.
In such a construction, however, since the variable angle prism is located in the convergent light, if the vertex angle of the prism is changed, decentering coma occurs largely.
Another example of the image-vibration compensation system for binoculars is disclosed in Japanese Laid Open Publication No HEI 6-308431. The binocular in the publication employs a compensation device that is attached in front of the objective optical systems of the binocular. Since the first lens of the objective optical system has the largest diameter in the telescopic optical system, in general, and the device is arranged in front of the first lenses, the device becomes large in size, which increases the size of the binocular.